This video demonstrates a sample that simulates a radar effect in a Silverlight based mapping application.

The weather data is real, its come from NOAA’s Nexrad Radar live feed.
http://www.arcgis.com/home/item.html?id=f78257e4db054611aca7693dd95a1eab

The Silverlight application is using Esri’s mapping technology.
http://www.esri.com/software/arcgis/web-mapping/silverlight.html